Andrew M. Westhoven1, Vince M. Davis1, Greg R. Kruger1, William G. Johnson1, Mark M. Loux2, and Jeff M. Stachler2. (1) Purdue Univ, Lilly Hall of Life Sciences, 915 W State St., West Lafayette, IN 47907, (2) The Ohio State Univ, Kottman Hall, 2021 Coffey Rd, Columbus, OH 43214
Indiana field surveys have shown that common lambsquarters (CLQ) escapes occur frequently in fields that contain glyphosate-resistant horseweed. In order to assess the sustainability of glyphosate-resistant cropping systems, problematic populations of this weed were subjected to in-field management studies to evaluate various control strategies. Fields were located by querying the 2003 horseweed survey database for fields that had CLQ and through discussions with crop advisors. These fields were sampled in the fall of 2005 and the weed seed was screened in the greenhouse for reduced sensitivity to glyphosate. A total of four field studies in Ohio and Indiana were investigated. Three different management systems were evaluated consisting of no burndown, burndown without a residual, and burndown plus a residual. Various postemergence treatments, timings, and rates were evaluated within each management system. Preliminary results indicate the burndown system effectively controlled all emerged CLQ at the time of application. The burndown plus residual system greatly reduced the number of CLQ at the time of postemergence applications compared to the other two systems. A few individual plants appear to be surviving an application of glyphosate at a rate of 0.84 kg ae/ha at most of the locations. CLQ control was improved using 1.68 kg ae/ha compared to 0.84 kg ae/ha in the no burndown and burndown with no residual systems.
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